We propose to continue our studies directed at understanding the molecular organization, function, and biosynthesis of cell membranes. With respect to molecular organization, we will investigate the possibility that the lipids of various membranes are asymmetrically distributed in the two halves of the lipid bilayer. We will use antibodies to phosphatidyl-inositol, cardiolipin, etc., to determine by immunoferritin techniques how these lipids are oriented in the membranes that contain them. The actomyosin-like components (the spectrin complex) attached to the erythrocyte membrane will be further investigated, to determined by immunoferritin techniques whether immunologically-related components are attached to the plasma membranes of other cells, such as lymphocytes, fibroblasts, etc. We propose also to investigate the biosynthesis of membranes, using a new method of specimen preparation for electron microscopy developed in our laboratory, frozen ultrathin sectioning. In conjunction with immunoferritin staining, this method allows us to detect and localize intracellular antigens, including those newly synthesized proteins that ultimately become components of plasma membranes.